1. Field of the Invention
The present invention relates to hydraulically operated rivet tools which clamp a workpiece and thereafter remove a rivet from or fasten a rivet into a workpiece.
2. Description of the Prior Art
Hydraulic rivet tools which sequentially clamp a workpiece and remove or fasten a rivet in the workpiece are well-known to those versed in the art. One type of these tools is provided with a pair of hydraulic cylinders as shown in Scott U.S. Pat. No. 1,767,946. In Scott one hydraulic cylinder, and the contained piston, provides the force necessary to bring the anvil toward and clamp the workpiece to the riveting set or die. The second hydraulic cylinder and contained piston provides the riveting force necessary to peen the rivet. While being adequate to fasten a rivet the use of two cylinders results in tools which require an entire cylinder to be dedicated to the clamping of the workpiece while a separate cylinder provides the riveting force. Furthermore the existence of separate cylinders necessitates complex interconnecting porting for the hydraulic fluid. The use of two hydraulic cylinders and pistons and the attendant porting requirements tended to make these types of machines not only costly but also cumbersome.
A second type of riveting machine provides for the dual use of one hydraulic cylinder as is shown in Rothe Patent 612,507. These tools, as in Rothe, provide for a first piston to extend from the cylinder to clamp the workpiece upon opening a first valve. A second valve is opened causing a second piston to extend from the first to engage the rivet. Once engaged the rivet is peened. This peening of the rivet is completed by the routing of the entire hydraulic fluid, including that used in clamping the workpiece, to the second piston. Even though providing a means to fasten a rivet, tools of this construction are of complex design, do not provide for a simple means whereby the tool can be changed from a rivet peen to a rivet punch, and do not provide for a constant clamping force since the total hydraulic pressure is routed to the rivet engaging piston near the end of its operation. Nor does the second piston contribute in any manner to the clamping of the workpiece. Its single function is to engage and peen the rivet.